Technology practices guidance is readily available to convey detailed information about the applicability of ISCO to varied contaminants and site conditions, conceptual design processes, design considerations, and implementation and performance monitoring. This page provides basic information on oxidant characteristics and identifies additional resources for planning and designing ISCO systems, monitoring system performance, and understanding the regulatory context of implementing an ISCO remedy.

Technology Planning and Design

Commonly used oxidants include potassium or sodium permanganate, Fenton's catalyzed hydrogen peroxide, hydrogen peroxide, ozone, and sodium persulfate. Each oxidant has advantages and limitations. The selection of an oxidant for site cleanup involves the following key concepts (EPA 2006a):

• Is the oxidant capable of degrading the contaminant of concern? Is a catalyst or other additive required to increase effectiveness?
• What is the soil oxidant demand (SOD)? SOD is a measure of how the naturally occurring materials in soil will affect the performance of some of the oxidants. For non-selective oxidants, high SOD will increase the cost of cleanup, as more oxidant will be required.
• What is the naturally occurring pH of the soil/groundwater system? Some oxidants require an acidic environment to work. If the soil is basic, an acid needs to be applied in addition to the oxidant.
• How will the decomposition rate of the oxidant affect application strategies? Some unreacted oxidants may remain in the subsurface for weeks to months, while others naturally decompose within hours of injection.

The type of delivery system selected depends upon the depth of the contaminants, the physical state of the oxidant (gas, liquid, solid), and its decomposition rate. Backhoes, trenchers, and augers have been used to work liquid and solid oxidants into contaminated soil and sludge. Liquids can be delivered either by gravity through wells and trenches or by injection. For vadose zones, gravity has the drawback of a relatively small area of influence and will require more injection points since the only driving force is hydraulic head which will limit horizontal spreading or limit it to the most permeable sections of the subsurface. Pressurized injection of liquids or gases, either through the screen of a well or the probe of a direct-push (DP) rig, will force the oxidant into the formation. The DP rig may offer a cost-effective way of delivering the oxidant, and if needed, the hole can be completed as a small-diameter well for later injections. Potassium permanganate and other solid-phase chemical oxidants have also been added by hydraulic or pneumatic fracturing (ITRC 2005, EPA 2006b).

The site stratigraphy plays an important role in the distribution of oxidants. Fine-grained units redirect oxidants to more permeable areas and are difficult to penetrate; hence, they can be the source of rebound later on as contaminants diffuse out. Long-lived oxidants (e.g., permanganate) have the potential to remain active as this diffusion occurs, and they can mitigate some of the potential rebound.

Chemical oxidation usually requires multiple applications (Siegrist et al. 2008, EPA 2006b, ITRC 2005). The table provides a qualitative list of oxidant reactivities with common site contaminants.

Source: ITRC 2005, Brown 2003, Watts 2011, and Root et al 2005
¹ Peroxide without a catalyst must be applied at higher concentrations, which are inherently hazardous, and the reactions are more difficult to predict and control.

In the special case of NAPLs, oxidants that are in a water-based solution will be able to react only with the dissolved phase of the contaminant, since the water solution and the hydrophobic NAPL will not mix. This property limits oxidation activity to the oxidant solution/NAPL interface. Cost estimates depend on the heterogeneity of the site subsurface, soil oxidation demand, stability of the oxidant, and type and concentration of the contaminant. Care should be taken when comparing different technologies on a cubic yard basis without considering these site attributes. Cost data can be found in ITRC (2005) and Brown (2003). In situ chemical oxidation has been used at dozens of sites, and oxidizing compounds are available from numerous vendors.

Sodium or Potassium Permanganate. Permanganate is a non-specific oxidizer of contaminants with low standard oxidation potential and high SOD. It can be used over a wide range of pH values and does not require a catalyst. Permanganate tends to remain in the subsurface for a long time, allowing for more contaminant contact and the potential of reducing rebound. As permanganate oxidizes organic materials, manganese oxide forms as a dark brown to black precipitate. During the treatment of large bodies of NAPL with high concentrations of permanganate, this precipitate may form a coating that reduces contact between oxidant and NAPL. The extent to which this reduction negatively affects contaminant oxidation has not been quantified (Siegrist et al., 2010, EPA 2006b, ITRC 2005). Potassium permanganate has a much lower solubility than sodium permanganate and generally is applied at lower concentrations. Commercial-grade permanganates may contain elevated concentrations of heavy metals, and they may lower the pH of the treated zone (U.S. EPA 2004). If bioremediation is planned as a polishing step, permanganate will have an adverse effect on microbial activity and may cause a change in microbe distribution. This effect is generally transitory (EPA 2006b). Also, there is some evidence that permanganates may be inhibitory to Dehalococcoides ethenogenes, the microbial species that completely dechlorinates PCE and TCE (Hrapovic et al. 2005).

Catalyzed Hydrogen Peroxide. Fenton's reagent or modified Fenton's reagent uses hydrogen peroxide in the presence of ferrous sulfate to generate hydroxyl radicals that are powerful oxidants. The reaction is fast, releases oxygen and heat, and can be difficult to control when high strength peroxide is used (ITRC 2005). Because of the fast reaction, the area of influence around the injection point is small. In conventional application, the reaction needs to take place in an acidified environment, which generally requires the injection of an acid to lower the treatment zone pH to between three and five. The reaction oxidizes the ferrous iron to ferric iron and if the subsurface pH is not acidic causes it to precipitate, which can result in a loss of permeability in the soil near the injection point (EPA 2006b). Over time, the depletion of the ferrous ion can be rate limiting for the process (EPA 2006b). Chelated iron can be used to preserve the iron in its ferrous state at neutral pH, thus eliminating the acid requirement. The byproducts of the reaction are relatively benign (EPA 2006b), and the heat of the reaction may cause favorable desorption or dissolution of contaminants and their subsequent destruction. Heat also may cause the movement of contaminants away from the treatment zone or allow them to escape to the atmosphere. Therefore, there are safety concerns with handling catalyzed hydrogen peroxide on the surface, and the potential exists for violent reactions in the subsurface. In many cases, there may be sufficient iron or other transition metals in the subsurface to eliminate the need to add ferrous sulfate.

Hydrogen Peroxide. While catalysts can be added to increase oxidation potential, hydrogen peroxide also can be used alone to oxidize contaminants. Peroxide oxidation is an exothermic reaction that can generate sufficient heat to boil water. The generation of heat can assist in making contaminants more available for degradation, as well as allowing them to escape to the surface. With its high reaction and decomposition rates, hydrogen peroxide is not likely to address contaminants found in low permeability soil. Solid peroxides (e.g., calcium peroxide) in slurry form moderate the rate of dissolution and peroxide generation, thereby allowing a more uniform distribution.

Ozone. One of the stronger oxidants, ozone can be applied as a gas or dissolved in water. As a gas, ozone can degrade a number of chemicals directly in both the dissolved and pure forms, and it provides an oxygen-rich environment for contaminants that degrade under aerobic conditions. It also degrades in water to form radical species that are highly reactive and non-specific. When ozone is introduced via the gas phase, the application rate is controlled by the phase equilibrium between gases and liquids. Because of this, ozone may require longer injection times than other oxidants, and vapor control equipment may be needed at the surface (ITRC 2005, EPA 2006b, ESTCP 2010). Because of its fast reactivity, ozone may not be appropriate for slow diffusion into low-permeability soil as it will be spent before it has the opportunity to diffuse.

Sodium Persulfate. Persulfate is a strong oxidant with a higher oxidation potential than hydrogen peroxide and a potentially lower SOD than permanganate or peroxide. Persulfate reaction is slow unless placed in the presence of a catalyst, such as ferrous iron, or heated to produce sulfate free radicals that are highly reactive and capable of degrading many organic compounds. At temperatures above 40°C, persulfate becomes especially reactive and can degrade most organics (Block et al. 2004). Like catalyzed hydrogen peroxide, the ferrous iron catalyst (when used) will degrade with time and precipitate (EPA 2006b). Persulfate also can be activated in the presence of base conditions (pH 12). The aquifer can be made basic by the addition of a strong alkali hydroxide such as potassium or sodium hydroxide. Persulfate activation decreases as the pH falls (from 12) but does not stop even at a pH of 8 (Miraglio 2009).

Technology Advantages (Adapted from EPA 2004)

• Contaminant mass can be destroyed in situ.
• Rapid destruction/degradation of contaminants (measurable reductions in weeks or months).
• Produces no significant wastes.
• Reduced mobilization, operation, and monitoring costs due to rapid results as compared with technologies such as pump and treat.
• Compatible with post-treatment monitored natural attenuation.
• Has potential to enhance aerobic and anaerobic biodegradation of residual hydrocarbons as part of a subsequent bioremediation or monitored natural attenuation program.
• Unlikely to disturb site operations.

Technology Limitations (Adapted from EPA 2004)

• Contamination in low permeability soils may not be readily contacted and destroyed by chemical oxidants; however, persulfate and permanganate can have longer activities in the subsurface and may be useful for destruction of back-diffusing chemicals and direct diffusion into low permeability soils.
• Catalyzed hydrogen peroxide can produce a significant quantity of explosive offgas. Un-reacted ozone may escape to the surface. Special precautions can be required for appropriate implementation of remedial action involving ozone or Fenton's chemistry.
• Dissolved contaminant concentrations may rebound weeks or months following chemical oxidation treatment, and require retreatment.
• Dissolved contaminant plume configuration may be altered by chemical oxidation application (e.g., displacement without treatment).
• Significant health and safety concerns are associated with handling and applying oxidants.
• Significant losses of chemical oxidants may occur as they react with soil/bedrock material rather than contaminants.
• Potential reduction of subsurface permeability. Permanganate may significantly alter aquifer geochemistry, which can cause clogging of the aquifer through precipitation of minerals in pore spaces. Other oxidants that use ferrous iron as an activation agent can cause the precipitation of ferric iron when acidic conditions are not maintained, which can reduce the permeability of the soil.

ISCO performance at any given site is dependent upon the contact achieved between the oxidant and the contaminants, which in turn is controlled by the NAPL architecture and other site-specific conditions. Oxidation technologies have the potential for achieving significant mass destruction of organics in the subsurface; however, the results of field and laboratory work indicate that complete removal of DNAPL may not be achieved with these technologies even under optimal conditions (NRC 2004). For DNAPL treatment, ISCO is typically combined with other pre-treatments, such as DNAPL extraction, and post-treatments, such as enhanced reductive dechlorination or monitored natural attenuation (ITRC 2005). Innovators are combining the benefits of ISCO implementation with compatible technologies, such as solvent flushing and bioremediation, to maximize remediation potential.

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References:

Block, P., R. Brown, and D. Robinson. 2004. Novel activation technologies for sodium persulfate in situ chemical oxidation. Proceedings of the Fourth International Conference on the Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA.

Brown, R. 2003. In situ chemical oxidation: performance, practice, and pitfalls. 2003 AFCEE Technology Transfer Workshop, February 25, 2003, San Antonio, TX.

Hrapovic, L. et al. 2005. Laboratory study of treatment of trichloroethene by chemical oxidation followed by bioremediation. Environmental Science & Technology, Vol 39 No 8, p 2888-2897.

ITRC. 2005. Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd Edition.

Miraglio, M.A. 2009. Base-Activated Persulfate Treatment of Contaminated Soils with pH Drift from Alkaline to Circumneutral. Master's thesis, Washington State University.

National Research Council (NRC), 2004. Contaminants in the Subsurface: Source Zone Assessment and Remediation. National Academies Press, Washington, DC.

Root, D.K. et al. 2005. Investigation of Chlorinated Methanes Treatability Using Activated Sodium Persulfate. Proceedings of the First International Conference on Environmental Science and Technology.

ESTCP. 2010. In Situ Chemical Oxidation for Groundwater Remediation: Technology Practices Manual. Environmental Security Technology Certification Program, Project ER-200623, CD-ROM, 2010 Request a CD of the manual

Siegrist, Robert, et al.. 2008. In Situ Chemical Oxidation for Remediation of Contaminated Groundwater: Summary Proceedings of an ISCO Technology Practices Workshop. ESTCP, ER-0623, 74 pp, 2008

U.S. EPA. 2004. How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers, EPA 510/R-04/002. Office of Underground Storage Tanks.

U.S. EPA. 2006a. In Situ Treatment Technologies for Contaminated Soil: Engineering Forum Issue Paper. EPA 542-F-06-013.

U.S. EPA. 2006b. In Situ Chemical Oxidation: Engineering Issue Paper, EPA 600-R-06-072

Watts, R.J. 2011. Enhanced Reactant-Contaminant Contact through the Use of Persulfate In Situ Chemical Oxidation (ISCO). SERDP Project ER-1489, 290 pp, 2011

Technical Resources

Technology Status Review: In Situ Oxidation
ESTCP, 50 pp, 1999

Results from a survey of ISCO implementation at government sites are summarized to help establish the basis for selecting and designing the technology; assess its costs and performance at specific sites; assess the reasons for ISCO success or failure; and provide guidance on use of the technology, including data requirements.

Principles and Practices of In Situ Chemical Oxidation Using Permanganate
2001. Siegrist, R.L.; M.A. Urynowicz; O.R. West; M.L. Crimi; K.S. Lowe. Battelle Press, Columbus, OH, ISBN:1-57477-102-7, 336 pp.

ITRC Technical and Regulatory Guidance for in Situ Chemical Oxidation of Contaminated Soil and Groundwater, Second Edition
2005. Interstate Technology and Regulatory Council (ITRC). ISCO-2, 171 pp.

Chemical Oxidation
2004. Chapter XIII in How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers. U.S. EPA, Office of Underground Storage Tanks, EPA 510-R-04-002, 52 pp.

Contaminants in the Subsurface: Source Zone Assessment and Remediation
National Research Council, Committee on Source Removal of Contaminants in the Subsurface. National Academies Press, Washington, DC. ISBN: 030909447X, 383 pp, 2004

After discussing the definition of 'source zone' and the characterization thereof, this report reviews the suite of technologies available for source remediation and their ability to reach a variety of cleanup goals, from meeting regulatory standards for ground water to reducing costs. The report proposes elements of a protocol for accomplishing source remediation that should enable project managers to decide whether and how to pursue source remediation at their sites.

Base-Activated Persulfate Treatment of Contaminated Soils with pH Drift from Alkaline to Circumneutral
Miraglio, M.A., Washington State University Master's Thesis, 38 pp, 2009

Experiments on persulfate activity show that when pH falls below 12, some activity remains.

Improved Understanding of Fenton-Like Reactions for the In Situ Remediation of Contaminated Groundwater, Including Treatment of Sorbed Contaminants and Destruction of DNAPLs
R.J. Watts, F.J. Loge, and A.L. Teel.
Strategic Environmental Research and Development Program (SERDP), 276 pp, 2006

Investigation of the processes and mechanisms associated with the use of catalyzed hydrogen peroxide propagations (CHP, or modified Fenton's reagent) for ISCO shows that superoxide has a major role in the degradation of highly oxidized contaminants, the destruction of DNAPLs, and the enhanced desorption of hydrophobic contaminants from soils and subsurface solids. The suite of reactive oxygen species generated in CHP reactions, including hydroxyl radical, superoxide, and the strong nucleophile hydroperoxide, provide a near-universal treatment matrix for chemical contaminants. This report discusses the applicability of modified Fenton's to the destruction of carbon tetrachloride, chloroform, benzo[a]pyrene, hexadecane, 1,1,1-TCA, 1,2-DCA, PCE, and TCE.

Technical Report: Subsurface Injection of In Situ Remedial Reagents (ISRRs) within the Los Angeles Regional Water Quality Control Board Jurisdiction
Wilson, S., D. Clexton, C. Sandefur, et al.
In Situ Remediation Reagents Injection Working Group, 46 pp, 2009

This compilation of general tools and best practices provides a reference manual for the planning, design, and field implementation phases of ISCO projects, with a strong emphasis on safety considerations. Specific attention is given to avoiding the visible surfacing of injected ISRR materials, minimizing impact to landscaping, and ensuring no surface pathway for potential ISRR runoff.

Enhanced Reactant-Contaminant Contact through the Use of Persulfate In Situ Chemical Oxidation (ISCO)
Watts, R.J.
SERDP Project ER-1489, 290 pp, 2011

This report describes the results of an investigation of the activation and persistence of persulfate in the subsurface to evaluate the potential for contact between the oxidant source and contaminants. Results showed that most minerals do not activate persulfate, particularly in the concentrations commonly found in the subsurface. Iron chelate-activated persulfate and base-activated persulfate generate hydroxyl radical, sulfate radical, and reductants, and provide the basis for widespread treatment of different classes of contaminants in the subsurface. Many organic compounds activate persulfate, including phenoxides and ketones. Because soil organic matter contains phenolic and ketonic components, it is a potent activator of persulfate. Depending on the acidity of the soil organic matter, it could activate persulfate with minimal addition of base. Persulfate has minimal effects on the mineralogy of the subsurface, with the exception of aging ferrihydrite. It can increase the permeability of some subsurface materials. Activated persulfate is a highly reactive remediation system that has sufficient longevity and transport characteristics to treat contaminants in low permeability regions of the subsurface.

Design Tool for Planning Permanganate Injection Systems: User's Guide
R. Borden, T. Simpkin, and M.T. Lieberman.
ESTCP Project ER-0626, 90 pp, 2010

This user's guide has been developed to accompany a simple Excel spreadsheet-based tool to assist in the design of permanganate injection systems for treatment of contaminated aquifers. The design tool will allow engineers to evaluate the effect of different design variables (well spacing, amount of reagent, injection rate, etc.) on remediation system cost and expected performance. The Excel spreadsheet, labeled 'Guidance Document,' is available on the SERDP-ESTCP website at the bottom of the page for Project ER-200626.

Efforts to Improve Coupled In Situ Chemical Oxidation with Bioremediation: A Review of Optimization Strategies
Sutton, N.B., J.T.C. Grotenhuis, A.A.M. Langenhoff, and H.H.M. Rijnaarts.
Journal of Soils and Sediments 11(1):129-140(2011)

The purpose of this review is to integrate recent results on coupled ISCO and bioremediation with the goal of identifying parameters necessary to an optimized combined treatment and areas that require additional focus.

Improved Understanding of In Situ Chemical Oxidation
P. Tratnyek, R. Waldemer, and J. Powell (I); and N.R. Thomson, X. Xu, and K. Sra (II).
SERDP ER-1289, 2009

Aquifer materials from 9 sites were characterized and evaluated with respect to their physiochemical properties and total theoretical and experimental reductive capacities. Batch and column experiments conducted with permanganate, persulfate, and Fenton's reagent evaluated fundamental chemical properties affecting oxidant consumption, maximum NOD of aquifer materials, kinetic behavior, and oxidant transport. For permanganate consumption, total organic carbon determined the maximum NOD value, while amorphous iron along with the cation exchange capacity determined the permanganate consumption rate, thereby suggesting a means to optimize control of unproductive permanganate consumption by aquifer materials through multiple oxidant injection episodes. A proposed permanganate-COD test method was deemed superior to the dichromate COD test and also can estimate the maximum NOD for site screening and initial design purposes. Persulfate combines well with thermal treatment because persulfate exposure to high temperatures leads to the formation of highly reactive sulfate radicals in addition to the higher reaction rates typically induced by higher temperatures. For PCE, permanganate oxidation may be more favorable at lower temperatures. Results indicate that the use of batch test data for design is questionable because column experiments can provide more realistic aquifer material contact, that better mimic in situ conditions.

Investigation of Chlorinated Methanes Treatability Using Activated Sodium Persulfate
Root, D.K, E.M. Lay, P.A. Block, and W.G. Cutler.
Proceedings of the First International Conference on Environmental Science and Technology, 6 pp, 2005

This paper examines the reactivity of persulfate with chlorinated methanes using various activation mechanisms.

Petroleum Hydrocarbon Remediation by In-Situ Chemical Oxidation at Colorado Sites
Colorado Department of Labor and Employment, Division of Oil and Public Safety, 36 pp, 2007

This report summarizes the components of ISCO application and evaluates ISCO implementation and results at 20 petroleum-contaminated sites in Colorado. ISCO injections were conducted either alone or as a cleanup component using hydrogen peroxide (10 sites), Fenton's reagent (4 sites), persulfate and catalyst (1 site), hydrogen peroxide with persulfate and catalyst (1 site), and modified Fenton's reagent (4 sites). Results were evaluated to determine the effectiveness of the different ISCO products for remediation of BTEX and MTBE and to see which site-specific factors had the greatest influence on successful technology performance. Cleanup success (based on decrease in dissolved benzene concentration) was recognized at only 3 sites and potentially achieved at 2 others. The lack of success at most of the sites was attributed to insufficient site characterization and/or pilot testing, leading to inaccurate determination of oxidant delivery volumes and concentrations, the effective radius of influence, and vertical intervals to be treated.

Coupling Surfactants/Cosolvents with Oxidants for Enhanced DNAPL Removal: A Review
Dugan, P.J., R.L. Siegrist, and M.L. Crimi.
Remediation Journal, Vol 20 No 3, p 27-49, 2010

This paper provides a critical review of peer-reviewed scientific literature, non-reviewed professional journals, and conference proceedings that discuss the use of surfactants/cosolvents and oxidants, either concurrently or sequentially, for DNAPL mass removal.

Delivery and Mixing in the Subsurface: Processes and Design Principles for In Situ Remediation
Kitanidis, P.K. and P.L. McCarty (eds.).
Springer, New York. ISBN: 978-1-4614-2238-9. SERDP-ESTCP Environmental Remediation Technology, Vol. 4, 325 pp, 2012

This technology monograph describes the principles of chemical delivery and mixing systems and their design and implementation for effective in situ remediation. In situ technologies discussed include chemical oxidation, surfactant/cosolvent flushing, subsurface reactors, recirculation systems, PRBs, gas delivery via sparging, and intrinsic remediation in natural-gradient systems. Numerous case studies are provided. Table of contents and abstracts.

Design and Quality Assurance/Quality Control Considerations for In Situ Chemical Oxidation
Rosansky, S.
TM-NAVFAC EXWC-EV-1302, 28 pp, 2013

This document offers a framework for design submittals of in situ remedial systems using ISCO technology, including a summary of best practices for ISCO design, tips for appropriate QA/QC measures, and links to available standards and references.

Best Practices for Injection and Distribution of Amendments
Rosansky, S., W. Condit, and R. Sirabian.
TR-NAVFAC-EXWC-EV-1303, 81 pp, 2013

Although there are many reasons for the sub-optimal performance of an in situ technology (e.g., chemical oxidation, chemical reduction, and enhanced bioremediation), a common underlying factor appears to be the inability to achieve adequate distribution and contact between the reagents, substrates, and target contaminants. This document presents current best practices for introducing liquid- and solid-phase amendments into aquifers to improve the likelihood of adequate amendment distribution. Lessons learned from three Navy case studies are provided.

Field Demonstration, Optimization, and Rigorous Validation of Peroxygen-Based ISCO for the Remediation of Contaminated Groundwater: CHP Stabilization Protocol
Watts, R., A. Teel, R. Brown, and T. Pac.
ESTCP Project ER-200632, 99 pp, 2014

Although catalyzed hydrogen peroxide propagations (CHP) is the ISCO process with the most robust chemistry and potential for contaminant destruction, peroxide is unstable in the subsurface. Recent advances, however, show that the addition of sodium citrate, sodium malonate, and sodium phytate potentially can slow peroxide decomposition rates up to 50-fold. The optimal implementation of these stabilizers for use in CHP field applications is detailed in this guide and illustrated with two case histories.

Assessing the Potential for Metals Mobilization During the Application of In Situ Chemical Oxidation Technologies
Gardner , K.H., E. Hadnagy, B.A. Smith, K. O'Shaughnessy, R. Fimmen, D.K. Nair, and H.V. Rectanus.
SERDP Project ER-2132, 83 pp, 2015

This document is designed to help the reader evaluate site-specific metal mobilization potential, with design suggestions for minimizing and monitoring metals mobilization in an ISCO field event. The text contains a review of the fundamental science for subsurficial fate and transport of metals (As, Cr, Cu, Ni, Pb, Zn) in groundwater and the major ISCO technologies (persulfate, permanganate, and H₂O₂ oxidation). Additional resources: SERDP Final Project Report; ISCO Metals Byproduct Reference Guide and Interactive Database

Horizontal Remediation Wells
Appendix A in How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers
EPA 510-B-17-003, 47 pp, 2017

Horizontal directional drilling can be used to install horizontal remediation wells (HRWs) at cleanup sites. The technology uses specialized equipment to produce either a curved surface-to-surface well or a blind well. HRWs are able to access locations beneath surface obstructions and to place long well screens in contact with the contaminated area. The wells can be thousands of feet long, with hundreds of feet of well screen. The potential for HRWs to complement a site remedy is described with reference to air sparging, bioremediation, chemical injection, soil vapor extraction, hot air or steam injection, LNAPL removal, plume containment, injection of treated water, and sampling. A detailed overview is provided of equipment and procedures for drilling a horizontal remediation well. Additional information: The complete UST CAP review manual

Optimizing Injection Strategies and In Situ Remediation Performance
The Interstate Technology & Regulatory Council Optimizing Injection Strategies and In Situ Remediation Performance Team. Report No. OIS-ISRP-1, 180 pp, 2020

This guidance describes how treatment ineffectiveness can be avoided through effective upfront characterization and design. It also provides the state of the practice based on firsthand knowledge and experiences for a broad audience, including environmental consultants, responsible parties, federal and state regulators, and community and tribal stakeholders. The document is divided into sections including remedial design characterization; amendment, dose and delivery design; implementation and feedback optimization, regulatory perspectives, community and tribal stakeholder considerations, and case studies.

Persulfate-Based Oxidation Processes in Environmental Remediation
Zhu, M., Z. Bian, and C. Zhao. (eds.) Royal Society of Chemistry, Print ISBN: 978-1-83916-308-1, PDF eISBN 978-1-83916-633-4, ePub eISBN 978-1-83916-634-1, 349 pp, 2022

This book summarizes environmental applications for persulfate-based advanced oxidation processes (AOPs). Topics include new activation methods and mechanisms and using of advanced materials for activating persulfate-based AOPs. Table of contents and abstracts.

Performance Monitoring

The comprehensive table below provides recommendations for performance monitoring parameters at ISCO sites. Performance monitoring parameters are site specific and are typically chosen through the data quality objectives process. The typical objectives for monitoring ISCO performance are measurements of contaminant mass reduction and oxidant dispersion. Secondary objectives can be detection of potential heavy metal mobilization and physical/chemical changes in the aquifer.

Contaminant mass reduction can be determined directly by measuring the reduction in groundwater contaminant concentrations and soil core concentrations, or indirectly with surrogates or tracers. Concern has been expressed about sampling for contaminants of concern and degradation products when there is the possibility of the presence of active oxidant. If the goal of the sampling is to determine the concentration of the contaminants at the time of sampling, Huling (2011) recommends that the oxidant be quenched when the sample is taken using ascorbic acid or other oxidant neutralizer. Siegrist et al. (2008) suggest that solvent extraction (e.g., hexane) could be used to accomplish the same goal.

Surrogates, such as chloride from the destruction of chlorinated aliphatics and benzenes, carbon dioxide, and carbon isotopes, can be used to measure mass reduction. The partitioning interwell tracer technique and other tracer methods can be used to estimate DNAPL mass before and after an oxidation injection. Contaminant flux changes also can be useful in determining remediation success; however, depending on the DNAPL architecture, a reduction in contaminant mass is not always followed by a reduction in flux.

Oxidant dispersion is measured directly in perimeter and selected target zone wells by testing for unreacted oxidant. Groundwater surrogates that show the presence of oxidant reactions include sulfate (modified Fenton's reagent and persulfate); dissolved oxygen (ozone, peroxide, and modified Fenton's reagent); pH, especially when ferrous sulfate (modified Fenton's reagent and persulfate) is the catalyst; redox; and specific conductance. Geophysical techniques, such as cross-borehole radar and electrical resistivity (see abstracts below), can be used to provide a three-dimensional image of oxidant movement in the subsurface. These techniques can identify areas where the oxidant did not penetrate or areas that were bypassed entirely by the oxidant (ITRC 2005).

Changes in redox or pH conditions have the potential to mobilize naturally occurring metals. While these metals generally do not remain soluble as they move downgradient of the treatment area, they are typically monitored. Also, commercial grade permanganate can contain heavy metals, such as chromium, at concentrations that could be of concern (EPA 2006).

Major cations can be used to track changes in mineral composition due to oxidant treatment and in some cases to identify where oxidants, such as potassium and sodium in permanganate and persulfate solutions, have been.

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References:

Engineering Issue Paper: In Situ Chemical Oxidation. EPA 600-R-06-072, 60 pp, 2006

Ground Water Sampling at ISCO Sites - Oxidant Residuals and Sample Preservation Guidelines (PPT). Huling, Scott, National Association of Remedial Project Managers Kansas City, KS May 19, 2011

In Situ Chemical Oxidation for Remediation of Contaminated Groundwater: Summary Proceedings of an ISCO Technology Practices Workshop. Siegrist, R., B. Petri, F. Krembs, M. Crimi, S. Ko, T. Simpkin, and T. Palaia. ESTCP, Project ER-0623, 74 pp, 2008

Standard Methods for the Examination of Water and Wastewater, 18th Edition
American Public Health Association (APHA), American Water Works Association, and Water Environment Federation, 1992 Standard Methods commercial Web site

Strategies for Monitoring the Performance of DNAPL Source Zone Remedies Interstate Technology & Regulatory Council, 205 pp, 2004

SW-846 On-Line: Test Methods for Evaluating Solid Waste, Physical/Chemical Methods. U.S. EPA, Office of Resource Conservation and Recovery.

Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd Edition. Interstate Technology & Regulatory Council (ITRC). ISCO-2, 172 pp, 2005

Performance Monitoring Resources

Ground Water Sample Preservation at In-Situ Chemical Oxidation Sites: Recommended Guidelines
Ko, S., S.G. Huling, and B. Pivetz.
EPA 600-R-12-049, 16 pp, 2012

This issue paper provides background information and general guidelines for methods and procedures that can be used to detect whether an oxidant (permanganate or persulfate) is present in groundwater, to approximate the oxidant concentration, and to estimate and deliver the volume or mass of preservative (ascorbic acid) required to preserve the binary mixture groundwater sample. An appendix provides specific details regarding preservation procedures.

In Situ Treatment Performance Monitoring: Issues and Best Practices
EPA 542-F-18-002, 2018

The purpose of this issue paper is to describe how in situ treatment technologies may impact sampling and analysis results used to monitor treatment performance and provide best practices to identify and mitigate issues that may affect sampling or analysis. This paper discusses eight potential sampling or analytical issues associated with groundwater monitoring at sites where in situ treatment technologies are applied. These issues are grouped under three topic areas: Issues related to monitoring wells (Section 2); Representativeness of monitoring wells (Section 3); Post-sampling artifacts (Section 4).

Abstracts

Automated Geophysical Monitoring of In Situ Engineered Treatments

• View Abstract

DC Resistivity Monitoring of Potassium Permanganate Injected to Oxidize TCE In Situ

• View Abstract

Electrical Imaging of Tracer Migration at the Massachusetts Military Reservation, Cape Cod

• View Abstract

Electrical Monitoring of In Situ Chemical Oxidation by Permanganate

• View Abstract

A Rapid Spectrophotometric Determination of Persulfate Anion in ISCO

• View Abstract

Electrical Resistivity Imaging of a Permanganate Injection during In Situ Treatment of RDX-Contaminated Groundwater

• View Abstract

Groundwater Sampling at ISCO Sites: Binary Mixtures of Volatile Organic Compounds and Persulfate

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Regulation

Federal EPA initiatives to reduce regulatory (and legislative) barriers to the use of ISCO technology have been implemented as follows:

• Since 1992, EPA has been granting states the authority to implement the Treatability Exclusion Rule; the Research, Development, and Demonstration Permit Program; and the Subpart X Permit Program. Those authorities are granted to states to simplify the approval process for technologies and to allow flexibility in testing and demonstrating innovative treatment technologies (ITTs).
• To further promote the use of innovative technologies, in 1994 EPA revised its Treatability Study Sample Exclusion Rule (59 FR 8362) to allow treatability studies on up to 10,000 kg of media contaminated with nonacute hazardous waste without the requirement for permitting and manifesting.
• In addition, EPA encouraged streamlining RCRA permits and orders for ITT development and use and encouraged state adoption and streamlining of EPA authorization to administer the treatment study sample exclusion rule.
• In 1993, EPA issued the Superfund Response Action Contractor Indemnification Rule (58 FR 5972), designed to help contractors who use ITTs obtain lower deductibles on liability insurance.
• EPA's 1996 area of contamination (AOC) policy allows soils to be excavated, moved, treated, and redeposited within the AOC without triggering RCRA regulatory requirements (ITRC 2005).
• In December 2000, EPA issued a memorandum, Applicability of RCRA Section 3020 to In-Situ Treatment of Ground Water, which clarifies that reinjection of treated groundwater to promote in situ treatment is allowed under section 3020(b), as long as certain conditions are met. Specifically, the groundwater must be treated prior to reinjection; the treatment must be intended to substantially reduce hazardous constituents in the ground water � either before or after reinjection; the cleanup must be protective of human health and the environment; and the injection must be part of a response action under CERCLA section 104 or 106 or a RCRA corrective action intended to clean up the contamination.
• EPA's Underground Injection Control (UIC) Program is responsible for regulating the construction, operation, permitting, and closure of injection wells that place fluids underground for storage or disposal. The UIC website offers guidance to inform state regulators and owners and operators of injection wells on how to operate injection wells safely to prevent contamination of underground drinking water resources.

Individual state regulations may be more restrictive than EPA requirements.

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Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd Edition. Interstate Technology & Regulatory Council (ITRC). ISCO-2, 172 pp, 2005